Radio access networks (RANs) provide for radio communication links to be arranged within the system between a plurality of user terminals. Such user terminals may be mobile and may be known as ‘mobile stations’ or ‘subscriber devices.’ At least one other terminal, e.g. used in conjunction with subscriber devices, may be a fixed terminal, e.g. a control terminal, base station, repeater, and/or access point (hereinafter, “base station”). Such a RAN typically includes a system infrastructure that generally includes a network of various base stations, which are in direct radio communication with the subscriber devices. Each of the base stations operating in the RAN may have one or more transceivers which may, for example, serve subscriber devices in a given local region or area, known as a ‘cell’ or ‘site’, by radio frequency (RF) communication. The subscriber devices that are in direct communication with a particular base station are said to be served by the base station. In one example, all radio communications to and from each subscriber device within the RAN are made via respective serving base stations. Sites of neighboring base stations may be offset from one another or may be non-overlapping or partially or fully overlapping.
RANs may operate according to an industry standard protocol such as, for example, the Project 25 (P25) standard defined by the Association of Public Safety Communications Officials International (APCO), or other radio protocols, such as the TErrestrial Trunked RAdio (TETRA) standard defined by the European Telecommunication Standards Institute (ETSI) or the Digital Mobile Radio (DMR) standard also defined by the ETSI, as well as others. Communications in accordance with any one or more of these standards, or other standards, may take place over physical channels in accordance with one or more of a TDMA (Time Division Multiple Access), FDMA (Frequency Division Multiple Access), OFDMA (Orthogonal Frequency Division Multiple Access), or CDMA (Code Division Multiple Access) protocol. Subscriber devices in RANs such as those set forth above send user communicated speech, video, audio, and/or data, herein referred to collectively as ‘traffic information’, in accordance with the designated protocol.
Land mobile radio (LMR) RANs may operate in either a conventional or trunked configuration. In either configuration, a plurality of subscriber devices are partitioned into separate groups of subscriber devices. In a conventional system, each subscriber device in a group is selected to a particular frequency for communications associated with that subscriber device's group. Thus, each group is served by one channel, and multiple groups may share the same single frequency (in which case, in some embodiments, signaling in the form of group IDs may be present in the broadcast data to distinguish between groups using the same shared frequency).
In contrast, a trunked radio system and its subscriber devices use a pool of traffic channels for virtually an unlimited number of groups of subscriber devices (e.g., talkgroups). Thus, all groups are served by all channels. The trunked radio system works to take advantage of the probability that not all groups need a traffic channel for communication at the same time. When a member of a group requests a call on a control or rest channel on which all of the subscriber devices in the system idle awaiting new call notifications, in one embodiment, a call controller assigns a separate traffic channel for the requested group call, and all group members move from the assigned control or rest channel to the assigned traffic channel for the group call. In another embodiment, when a member of a group requests a call on a control or rest channel, the call controller may convert the control or rest channel on which the subscriber devices were idling to a traffic channel for the call, and instruct all subscriber devices that are not participating in the call to move to a newly assigned control or rest channel selected from the pool of available channels. With a given number of channels, a much greater number of groups can be accommodated in a trunked system as compared with conventional radio systems.
One possible LMR protocol, for example, is the ETSI-DMR standard, which is a direct digital replacement for analog Private Mobile Radio (PMR). DMR is a scalable system that can be used in unlicensed mode (in certain allocations within certain regions or countries), and in licensed mode, subject to national or regional frequency planning.
DMR promises improved range, higher data rates, more efficient use of spectrum, and improved battery life. Features supported include fast call set-up, calls to groups and individuals, short data and packet data calls. Supported communications modes include individual calls, group calls, and broadcast calls provided among the radios operating within the network. Other important DMR functions such as emergency calls, priority calls, short data messages and Internet Protocol (IP) packet data transmissions are also supported.
The ETSI-DMR standard provides for 6.25e (2:1 TDMA) operation in repeater mode. 6.25e operation refers to 6.25 Kilohertz (kHz) equivalent spectral efficiency and 2:1 refers to the slotting ratio supported on the TDMA air interface, in this case supporting two repeating (e.g., recurring) interleaved time slots. As there is no restriction on what happens in either time slot or any interrelation between them (other than the need to maintain time synchronicity), it is possible to have two entirely separate conversations at the same time from two different units.
ETSI-DMR is just one example, and other trunked or conventional LMR protocols (such as APCO P25 or TETRA) could be used as well.
For any of the above-mentioned protocols, corresponding ‘public safety’ RANs provide for group-based radio communications amongst a plurality of subscriber devices such that one member of a designated group can transmit once and have that transmission received by all other members of the group substantially simultaneously. Groups are conventionally assigned based on function. For example, all members of a particular local police force may be assigned to a same group so that all members of the particular local police force can stay in contact with one another, while avoiding the random transmissions of radio users outside of the local police force group.
When an event or incident occurs, such as a fire or accident, numerous different groups may respond to the incident, including for example, direct first responders such as police, fire, and medical groups and supporting responders such as utility, traffic control, crowd control groups, among others.
One problem that may occur in any of the above radio systems in which an infrastructure repeater is being used to repeat communications received on an uplink channel between a subscriber device and its serving base station (via either a trunked or conventional uplink traffic channel), is that uplink-transmitting subscriber devices close to the serving base station may over-power and/or interfere with other uplink-transmitting subscriber devices farther away from the serving BS when those uplink traffic channels are immediately adjacent one another on the frequency spectrum.
Historically, in the United States and worldwide, excessive guardbands between adjacent channels were instituted to prevent interference between those adjacent channels. However, due to increased demand for radio bandwidth and a desire to increase efficient use of the radio spectrum, guardbands have been shrinking across most of the spectrum.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.